Process for producing negative working offset diazo printing plates



April 1964 c. E. HERRICK, JR.. ETAL 3,130,051

PROCESS FOR PRODUCING NEGATIVE WORKING OFFSET DIAZO PRINTING PLATES Filed Dec. 10, 1958 OVERCOATING OF HIGH MOLECULAR 3-i/// WEIGHT WATER SOLUBLEDIAZONIUM COMPOUND- 2 LACQUER LAYER OF COPOLYMER G BASE FIGJ

GREASE-RECEPTIVE PRINTING AREAS PHOTOPOLYMERIZED DIAZONIUM COMPOlND K HYDROPHILIC PORTIONS OF LACQUER LAYER 2 1 WW LACQUER LAYER OF COPOLYMER OF VINYL ETHER AND MALEIC ANHYDRIE BASE FIG.2

IN VENTORS CLIFFORD E.HERRICK, JR. PAUL CHE BINIAK Z/ 4263 4" ZZZ, figm A TTORNEYS United States Patent 3,130,051 PROiIESS FOR PRODUCENG NEGATIVE WGRKING ()FFSET DIIAZG PRZNTING PLATES Clifford E. Herrick, Jr., Chenango Forks, and Paul (Ihehiniak, Binghamton, N.Y., assignors to General Aniline & Film Corporation, New York, N.Y., a corporation of Delaware Filed Dec. 10, 1958, Ser. No. 779,489 8 Claims. (Cl. 9649) The present invention pertains to negative working offset plates comprising a water-soluble diazo sensitizer coated on a substrate containing a copolymer of a vinyl ether and maleic anhydride.

Presensitized negative working paper plates have been manufactured and sold for a number of years. They have found wide acceptance in the so-called offset duplicator field of lithography because of their low cost and convenience to the user. Such plates, in general, have a rather complex structure. For instance, U.S. Patent 2,766,688 describes a material in which five or more separate coatings are laid down on a base material to produce a presensitized negative working plate. This procedure, within the limits of resolution imposed by the grainy structure introduced by a pigment, produces excellent copy but it is manifestly not a simple article to manufacture.

In addition, it is ditficult to conveniently make additions, deletions, or corrections on some of the commercial plates. For instance, the plate described in U.S. Patent 2,692,827 requires long exposure and may tend to be slow printing when afiixed to an offset duplicator. By slow printing is meant that the image areas of the processed plate may require many revolutions past the ink roller before these image areas take enough ink to produce suitable copy. This is especially evident in the case of plates that have been stored for a. considerable length of time before use.

It is manifest, therefore, that room exists for improvements in the area of inexpensive presensitized negative Working plates.

U.S. Patent 2,772,972 describes a novel positive Working offset plate comprising a base 1 on the surface of which is coated a lacquer layer 2 of an alkyl vinyl ether copolymerized with maleic anhydride and, if desired, a suitable hydrophobic resin such as cellulose acetate, the lacquer layer being overcoated with a layer 3 of a waterinsoluble, light-sensitive diazooxide and an adhesive resin. In order to produce an ink-repellent hydrophilic condition on the lacquered surface 2 in the areas where the plate is exposed under a pattern, a treatment with a polyhydric alcohol and an alkylolamine is required. Thus, the exposed areas are removed by the polyhydric alcohol and the lacquer layer 2 where bared is rendered hydrophilic by the alkylolamine.

The plates of U.S. Patent 2,772,972 have found wide acceptance in the duplicating trade, not only by virtue of the fact that they yield a positive from a positive, thus opening the way to high speed duplication of translucent originals, but also because of the excellent contrast and printing qualities afforded by the base lacquered with a vinyl ether/maleic anhydride copolymer. The low selling price which the simple manufacturing process permits is notably advantageous. It would clearly be of interest to produce a light-sensitive negative working plate having the excellent properties peculiar to the positive plate of said patent.

It is an object of this invention to produce a negative working plate by relatively uncomplicated and inexpensive means.

It is a further object to produce a plate having good light sensitivity, good shelf life and a grainless surface so that high quality half-tones can be produced, and which is possessed of high sensitometric contrast so that satisfactory copies can be produced from relatively poor negative originals.

It is a further object of this invention to produce a sensitized plate capable of being produced on a surface similar to that described in U.S. Patent 2,772,972 and processed with essentially the same techniques.

It is a further object to produce a plate having a grainless surface which, however, is capable of accepting addi tional information and which permits easy corrections and deletions, both in image and non-image areas.

We have found, unexpectedly, that if a water soluble diazonium compound such as those described in U.S. Patent 2,773,779 be coated wholly upon the vinyl ether/ maleic anhydride lacquered surface of the base material described in U.S. Patent 2,772,972 and thereafter the plate be exposed to light beneath a negative pattern, the lightstruck portions become insolubilized to the type of developer described in U.S. Patent 2,772,972 when modified by the addition of a hydrophobic substance as subsequently described and become firmly bound to the lacquered surface, and the non-light-struck portion is entirely removed by the action of such modified developer, water sensitivity being induced in the lacquer layer in an imagewise manner. In order to make the developers of U.S. Patent 2,772,972 suitable for use with water-soluble diazonium salt sensitizers, we have found it highly advantageous to add to the developer mixture a substantial fraction of a hydrophobic substance, for example, oleic acid. We have noted, to our surprise, that such developers have the property of hydrolyzing the lacquer layer thoroughly at the exposed portions thereof.

Typically, we provide a plate having the layers 1 and 2 of U.S. Patent 2,772,972 and in lieu of layer 3 of said patent, an overcoat on the surface of layer 2 of a Watersoluble diazonium compound such as the product from reacting p-anilinobenzenediazonium sulfate with formaldehyde. The plate so constituted is then exposed under a negative pattern. The plate is developed by use of, for instance, 5 parts by weight of the aforesaid positive plate developer of U.S. Patent 2,772,972 containing 63.5% ethylene glycol, 25% glycerin, 10% diethanolamine and 1.5% monoethanolamine to which is added 1 part oleic acid. Th s developer gives good development for the negative plates. In spite of the fact that nearly an equivalent of acid has been added to the active basic ingredients of the developer, this addition does not impair the ability of the developer composition to render the lacquer layer ink-repellent and hydrophilic.

It is apparent, therefore, that the developer in the present instance plays a role which may be considered the reverse of that played by the developer in U.S. Patent 2,772,972. Thus, whereas in the patent the developer removes layer 3 where it is light-struck and renders hydrophilic the lacquer layer in the light-struck areas, the present developer removes the areas of the outer layer which are not struck by light and renders the underneath lacquer layer hydrophilic in these areas. Typically, the p-am'linobenzenediazonium salt:formaldehyde polymer on the surface of the vinyl ether/maleic anhydride lacquer layer by the action of actinic light photopolymerizes, thereby insolubilizing the light-struck portions of the outer layer.

' In addition, it is thought that a cross-linking occurs at the interface between the photopolymerization product and the vinyl ether/maleic anhydride copolymer which bonds the image tenaciously to the base material. The photopolymerization product is thought to have a relatively porous structure since the light-struck areas tend to assume the characteristics of the material which first comes in contact with them. For instance, when the developing composition described in U.S. Patent 2,772,972,

which consists mainly of hydrophilic materials, is used on the plate, a film of these materials adheres to the porous image areas and causes these areas to become relatively blind and non-ink-receptive. When greasy materials such as a developing ink or developing lacquer are first applied to the plate, they become absorbed into the porous image areas, and subsequent treatment with the above-mentioned developing composition causes the lightstruck areas to become ink-receptive and the non-lightstruck areas to become water-receptive. When a greasy material such as oleic acid is incorporated into the developing composition and the exposed plate is processed with the mixture, the porous light-struck areas appear to preferentially absorb the greasy material and make them water repellent while the other components of the developing composition act to expose and hydrolyze the lacquered base in non-light-struck areas and render them water-receptive.

It should again be noted that treatment with a base during development is required in order to render the lacquer surface non-printing in the non-image areas. However, the bases required, for instance, need not be free bases. By this is meant that the base may be combined in the form of an amine soap. In one preferred modification of this invention, the developer composition contains 0.1 mol of amine and 0.063 mol of oleic acid, making the elfective concentration of free base only 0.037 mol, or an effective concentration of slightly more than /3 of the original concentration of amine found necessary to eifectively render non-image areas hydrophilic on the positive plate, as practiced in US. Patent 2,772,972. Nevertheless, in the exploitation of this invention, this amount of amine was found to be entirely satisfactory. In effect, under these circumstances, it appears that the amine soap will hydrolyze sufiiciently into an amine and oleic acid to effectively perform their separate functions.

The present invention will be better understood by reference to the accompanying drawing, FIG. 1 of which is a sectional view of the plate before processing and FIG. 2 of which is a similar view of the plate subsequent to processing.

Referring to the drawing and particularly to FIG. 1 thereof, it will be seen that the raw plate comprises a base bearing a lacquer substratum 2 having an outer coating 3 of a water-soluble, light-sensitive diazonium compound.

The base 1 is made of a relatively inexpensive fibrous material such as paper, cloth or the like. It will be apparent, however, that the specific nature of this base material is not a critical feature of the invention since any relatively inexpensive fibrous material capable of accepting and retaining the lacquer layer 2 is suitable.

The lacquer layer 2 contains as its essential element a copolymer of a vinyl ether and maleic anhydride in substantially equimolar proportions. Such copolymers are described in US. Patent 2,047,398, granted July 14, 1936, and are available on the open market.

We find that, while said plates can be produced where the layer 2 consists of the vinyl ether/maleic anhydride copolymer, best results are achieved when said layer 2 is composed of a solid solution of the copolymer and a hydrophobic resin compatible therewith. The hydrophobic resin serves the function of imparting toughness and flexibility to the plate and of eliminating tendencies of the layer 2 to'crack or craze. Where the hydrophobic resin is used, it may be present in the lacquer layer in a quantity as high as 60% of the lacquer layer. For best results, however, the quantity of the hydrophobic resin should not exceed 40% by weight of the solid content of the lacquer layer 2.

Where a hydrophobic resin is used in the lacquer layer, the lacquer layer exists as a solid solution of the copolymer and said hydrophobic resin which is compatible with the copolymer. Compatibility of the resins is, of course, a condition precedent to the obtaining of a true solid solu tion and not a heterogeneous mixture of the resins. It is s patent that the latter would offer a variable surface to the processing solutions, thus leading to non-uniformity in the creation of hydrophilic character in said layer.

Hydrophobic resins compatible with the copolymer include the various cellulose esters such as cellulose acetate, cellulose propionate, cellulose butyrate, the mixed esters such as cellulose acetate-propionate, cellulose acetatebutyrate and the like, polyvinyl resins such as polyvinyl acetate, polyvinyl acetals such as polyvinyl butyral, poly (methyl acrylate), poly(methyl methacrylate) and the like.

Within the series of commercially available cellulose esters, grades which contain combined acetic acid from as low as 52% to as high as 61.8% (triacetate) can be employed. If a cellulose ester be used, it is recommended that it be of high acyl content, although satisfactory results accrue when a low acetylated product be employed. We have good reason to believe that since the maleic anhydride copolymers are reactive materials, they can, in the course of time, react with the unesterified hydroxyls of a low acyl ester. The result of such a reaction is usually a change in the degree to which the layer can be rendered hydrophilic. Thus, a freshly lacquered sample containing a low acyl cellulose ester may respond dilferently to the processing solution than a sample some weeks old. In any case, irrespective of the mechanism, we have found that greater uniformity and consistency of response are attained when cellulose esters of the highest degree of acylation are utilized. It should be further pointed out that when a high acyl cellulose ester is used, a relatively higher proportion of copolymer is required for optimum results than when a low acyl cellulose ester is employed.

The copolymer which is employed may be poly(vinyl methyl ether/maleic anhydride), poly(vinyl chloroethyl ether/maleic anhydride), poly(vinyl isopropyl ether/ maleic anhydride), poly(vinyl butyl ether/maleic anhydride) and poly(vinyl isobutyl ether/maleic anhydride).

Various solvents and solvent mixtures may be utilized for laying down the lacquer coating and, in this connection, attention is directed to the solvents described in US. Patent 2,756,163. Solvents which we have found to be suitable are liquid relatively low boiling organic solvents such as 2-methoxyethanol, acetone, methylene chloride, dioxane, tetrahydrofuran, cyclohexanone, methyl ethyl ketone and various mixtures of the same. Such mixtures include, for example, methylene chloride, 2- methoxyethanol and acetone, Z-methoxyethanol and di-v oxane, Z-methoxyethanol and cyclohexanone, Z-methoxyethanol and tetrahydrofuran and the like.

These solvents, because of their relatively low boiling point, are readily removed to yield a dry lacquer film.

This film generally has a thickness ranging from about .1 to .4 mil, preferably .2 mil.

It is to be pointed out that the sensitizer layer 3 need not necessarily be a high molecular weight condensation product although we prefer to use the same in our invention. The water-soluble, light-sensitive diazonium compounds, operable in our process, possess the following prerequisites:

(1) They contain light-sensitive groups contributing primarily to water solubility, e.g., a diazonium group(s).

(2) The light-sensitive molecule is fairly large, mainly containing at least two groups of the size of phenyl or substituted phenyl groups.

(3) The molecular fragment left when the light-sensitive group imparting water solubility has left the mole? cule tends to be reactive especially with molecules simi-. lar to itself so that a species of photopolymerization results.

(4) The sensitizers when used in our application yield positive copies from negative originals.

Suitable diazo compounds meeting the aforesaid prerequisites are those of the following formulae:

wherein R is a phenyl radical such as phenyl, halophenyl, i.e., bromophenyl, chlorophenyl or the like, carboxyphenyl, alkylphenyl, i.e., toluyl, ethylphenyl and the like, alkoxyphenyl, i.e., methoxyphenyl, ethoxyphenyl and the like, an aralkyl radical such as benzyl, chlorobenzyl, bromobenzyl and the like, cycloalkyl such as cyclohexyl or acyl, i.e., acetyl, lauroyl, benzoyl and the like; Y is O, S, NH or NR R being alkyl, i.e., methyl, ethyl, propyl or the like; Ar is an aromatic radical; X is an anion of an acid and R is imino or polyalkylene, i.e. dimethylene, trirnethylene or the like. Polymeric diazo compounds which are obtained by reacting the aforesaid diazo compounds with carbonyl compounds such as formaldehyde are preferred.

Examples of suitable diazo compounds within the ambit of the above formulae are:

The condensation product of p-anilinobenzenediazonium sulfate and formaldehyde p,p-Iminodibenzenediazonium chloride N-methyl-p-anilinobenzenediazonium chloride 2,5-diethoxy-4-lauramidobenzenediazonium chloride N,N trimethylenebis(p ethylaminobenzenediazonium chloride) p,p Iminodibenzenediazonium chloride reacted with formaldehyde N-benzyl-N-ethyl-p-aminobenzenediazonium chloride N 2,6 dichlorobenzyl N ethyl p aminobenzenediazonium chloride 2,5 diethoxy 4 (p ethoxyphenoxy)benzenediazonium chloride 4 (p bromoanilino) 2,5 dibromobenzenediazonium chloride p-(2,4,6-trichloroanilino)benzenediazonium chloride 4 anilino 3 (2,5 diethoxyphenylsulfamoyl)benzenediazonium chloride 2,5 dipropoxy 4 (p-tolylthio)benzenediazonium chloride The invention is further illustrated by the following examples, but it is to be understood that the invention is not restricted thereto.

Example I A 1% aqueous solution of a condensation product of p-anilinobenzenediazonium sulfate and formaldehyde was bead-coated onto the lacquered surface 2 of a wet strength clay-resin surfaced paper which had been coated and dried to yield a dry film thickness of about 0.3 mil with a lacquer of the following composition:

Following exposure for 30 seconds beneath a negative original in a vacuum frame at a distance of 18 inches from an arc consuming 35 amperes of current, the plate was swabbed for a few seconds with a pad moistened with a solution of the following composition:

Z-aminoethanol ml' 1.5 2,2'-2"-nitrilotriethanol ml 10.0 Glycerin rnl 25.0 Ethylene glycol ml 63.5 Gleic acid ml 20.0

The sensitizing layer thus was rapidly removed in regions of the plate which were protected during the exposure by opaque portions of the original. The completeness of this removal could be conveniently followed by the presence of color on the exposed surface since the nonlight-struck areas are yellow in color.

The above-mentioned developing process functions in several Ways. First, it serves to remove the non-lightstruck, light-sensitive coating and renders the plate insensitive to the further action of light. Secondly, the hydrophobic lacquer layer 2 is rendered hydrophilic in the non-light-struck areas. Thirdly, the fatty acid becomes physically attached to the tanned diazo resin layer 1 in the image areas to render these areas very hydrophobic and ink-receptive.

Upon completion of development it is desirable to swab the plate for several seconds with a pad moistened with a commercial acidic fixing solution of the type disclosed in US. Patent 2,772,972. The above-mentioned acidic fixer solution tends to neutralize the action of the basic developer and renders the plate suitable for use on an offset duplicator.

Upon being attached to the plate cylinder of an offset duplicator and starting the machine, the image areas of the plate become inked rapidly and good positive copies were obtained with excellent half-tone dot rendition and good ink density.

Example 11 The procedure was the same as in Example I excepting that the lacquer layer 2 was bead-coated with a 1% aqueous solution of N,N-trimethylenebis(p-ethylaminobenzenediazonium chloride). Upon being dried, a portion of the plate was exposed under a negative original for 30 seconds in a vacuum frame at a distance of 18" from an arc consuming 35 amperes of current. Following exposure, the plate was swabbed for a few seconds with the developing composition described in Example 1. Next, the plate was swabbed with a commercial acid fixing solution. Upon completion of this step, the plate was attached to the plate cylinder of an offset duplicator and positive copies of the original were obtained.

As the fixing solution one may use any acidified aqueous solution which in addition to an acid, e.g., phosphoric acid, may contain gum arabic, carboxymethyl cellulose, ethylene glycol, glycerin or any other suitable desensitizer. Indeed, it is not necessary that any fixing solution be applied to the plate since the fountain solutions in common use in lithography today contain basically the same materials employed in the commercial fixing solutions.

Example 1 1] A 1% aqueous solution of p,p'-iminodibenzenediazonium chloride was bead-coated on lacquer layer 2 of Example 1. Upon being dried, the Webwas cut into 10 x 15" plates, one of which was exposed for 30 seconds in a vacuum frame beneath a negative original at a distance of 18" from a carbon arc consuming 35 amperes of current. Following exposure, the plate was swabbed for a few seconds with a pad moistened with the developing solution described in Example I. The excess developing solution was conveniently removed with a dry pad and the plate was attached directly to the plate cylinder of an offset duplicator, while eliminating the application of the fixing solution described in the preceding examples. After the press Was started, positive copies of the original were obtained.

Example IV The procedure was the same as in Example 111 excepting that the sensitizer was a 1% aqueous solution of N- methyl-p-anilinobenzenediazonium chloride.

Example V The procedure was the same as in Example 111 excepting that the sensitizer was a 1% aqueous solution of N- benzyl-N-ethyl-p-aminobenzenediazonium chloride.

Example VI The procedure was they same as in Example HI excepting that the sensitizer was a 1% aqueous solution of a zinc chloride double salt of N,-N'-trimethylenebis (p-ethylaminobenzenediazonium chloride).

Example VII The procedure was the same as in Example I II excepting that the sensitizer was a 1% aqueous solution of 2,5- diethoxy-4-lauramidobenzenediazonium chloride.

Example VIII A 1% aqueous solution of a condensation product of p-anilinobenzenediazonium sulfate and formaldehyde was bead-coated onto the lacquered surface of a wet strength, clay-resin surfaced paper base 1 which had been coated and dried to yield a dry film thickness of about 0.3 mil with a lacquer of the following composition:

Following exposure for 30 seconds beneath a negative original in a'vacuum frame at a distance of 18" from an arc consuming 35 amperes of current, the plate was swabbed for between 1 and 2 minutes with the developing solution described in Example I, whereupon the sensitizing layer was removed in the regions of the plate which were protected during the exposure by opaque portions of the negative original. Upon completion of the developing step, the plate was swabbed for several seconds with a pad moistened with a fixing solution and then attached to the plate cylinder of an offset duplicator. Upon starting the duplicator, positive copies of the negative original were obtained.

Example IX Positive copies of a negative original were obtained from a plate made and processed in substantially the same manner described in Example VIII excepting that the base material 1 was lacquered with the following composition 7 to provide layer 2:

Acetone ml 45 Methyl ethyl ketone ml 45 2-methoxyethyl acetate ml Cellulose acetate g 2.0 Ethyl phthalate, ethyl glycolate g 1.4 Poly(vinyl chloroethyl ether/maleic anhydride) g 4.0 Acetone to' ml 100 Example X Positive copies of a negative original were obtained from a plate made and processed in substantially the same manner described in Example VIII excepting that the base 1 was lacquered with the following composition to provide layer 2:

Positive copies of a negative original were obtained from a plate made and processed in substantially the same manner as described in Example VIII excepting that the base material 1 was lacquered with the following composition to provide layer 2:

Acetone ml 45 Methyl ethyl ketone ml 45 2-methoxyethyl acetate ml 5 Cellulose acetate g 2.0 Ethyl phthalate, ethyl glycolate g 1.4 Poly(vinyl isobutyl ether/maleic anhydride) g 4.0 Acetone to m In all of the above-mentioned examples, oleic acid or a polymer thereof was used in the developer composition as described under Example I. Although these oleic acid products function very well to produce a physically adherent layer of hydrophobic material on the light-struck areas of the plate during the development process, there are many other fat-like or oil-like materials, either miscible or immiscible withthe other constituents of the developing solution, which perform the function of oleic acid, some better than the oleic acid itself. Indeed, oleic acid is not wholly desirable in that being an unsaturated fatty acid it is subject to oxidation and turns rancid, which limits shelf life. Among the classes of materials either solids or liquids which will serve to function in a manner similar to oleic acid are:

(1) Oils, i.e., mineral oil, castor oil, dehydrated castor oil (2) Waxes, i.e., aqueous dispersions of Carnauba waxes (3) Hydrophobic resins, i.e., silicone (4) Fatty acids, i.e., stearic and palmitic (5) Fatty acid esters, i.e., methyl ester of stearic acid,

palm oil (6) Dibasic fatty acid esters, i.e., diethyl ester of sebacic acid (7) Dibasic fatty acid half'esters, i.e., butyl ester of sebacic acid (8). Fatty alcohols, i.e., lauryl alcohol (9) Fatty quaternary ammonium chlorides, i.e., disoyabean dimethyl ammonium chloride (10) Fatty nitl'iles (ll) Tertiary olyoxyethylene amines, i.e., reaction products of soya-bean amine with 2 or 5 mols of ethylene oxide (12) Diamines of olyoxyethylene glycols, i.e., reaction product of 1 mol of coco amine or of tallow amine with 3 mols of ethylene oxide (13) Polyoxyethylene amides, i.e., reaction product of coco amide with 5 mols of ethylene oxide and reaction product of 1 mol of hydrogenated tallow amide with 50 mols of ethylene oxide (14) Inorganic acid esters, i.e., trioctyl phosphate and tributyl phosphate (15) Monofatty acid esters of polyoxyethylene glycols, i.e., reaction product of 1 mol of red oil fatty acid with 5 mols of ethylene oxide (16) Monoesters of glycerol, i.e., glycerol monoricinoleate (17) Monoesters of ethylene glycol, i.e., ethylene glycol monostearate (18) Polymerized fatty acids, i.e., dimerized and trimerized oleic acid Example XII The procedure was the same as in Example I excepting that the developer used had the following composition:

Z-aminoethanol cc 1.5 2,2-2"-nitrilotriethanol cc 10.0 Glycerin cc 25.0 Ethylene glycol cc 63.5 Dimerized oleic acid cc 20.0

Excellent positive copies were obtained from the negative original.

In lieu of the dimerized oleic acid, equally good results are obtained by using trimerized oleic acid;

Example XII] The procedure was the same as in Example I excepting that the oleic acid in the developer was replaced by ml. of any one of the following fatty acid mixtures:

iii It should be pointed out that the inorganic acid esters were not miscible with the other components of the developer. However, this was found to be of little consequence since the only requirement is that the fatty sub- 9/11 Wochem Palmitic Stearic Ricin- Oleic Linoleic Lin- Elaeo- Octadec- No. oleic olenic stearic andienic (Combined) Castor Fatty Acid 110 Chinawood Fatty Acid. 400 3 Conjugated Linseed Oil 711 10 Corn Fatty Acid 220 11 5 Cotton Fatty Acid, Sunra Distilled 410 3 Distollne" Fatty Acid 120 9 Helioline A Fatty Acid 420 9 Isoline Fatty Acid, Supra 430 Palm Fatty Acid, Double Distilled 281 45 6 40 9 High Titre Vegetable Fatty Acid 230 40 5 25 Example XIV stance be relatively uniformly dispersed with the other The procedure was the same as in Example I excepting that the oleic acid was replaced by an equivalent quantity of fatty alcohols. One desirable feature of using the fatty alcohols in place of the fatty acids as per this example is that the eifective concentration of the amines is not reduced and is available to more completely hydrolyze the lacquer layer 2.

Example XV The procedure was the same as in Example I excepting that the oleic acid was replaced by an equivalent quantity of the reaction products of soya-bean amine with 2 or 5 mols of ethylene oxide.

Good positive copies were obtained from a negative original on an ofiset duplicator.

Example XVI The procedure was the same as in Example I excepting that the oleic acid was replaced by an equivalent quantity of the monofatty acid esters of polyethylene glycols identified below:

Source of Alkyl Avg. Mol Mols of Radical Wt. Ethylene Oxide Ethot'at 142/20 Red oil fatty acid 726 10 Ethoiat 142/15 do 506 5 Example XVII The procedure was the same in Example I excepting that the oleic acid was replaced by linseed oil. Good positive copies were obtained from a negative original.

In lieu of the linseed oil, there may be employed mineral oil, castor oil, dehydrated castor oil and styrenated dehydrated castor oil.

Example X VIII The procedure was the same as in Example I excepting that the oleic acid was replaced with an equal amount of trioctyl phosphate. Good positive copies were obtained from a negative original.

In lieu of the trioctyl phosphate one may also use tributyl phosphate.

components in order to perform satisfactorily.

Example XIX The procedure was the same as in Example I excepting that the oleic acid in the developing solution was replaced by 20 cc. of silicone resin.

Good positive copies of a negatiev original Were thus obtained.

Example XX The procedure was the same as in Example I, excepting that the oleic acid in the developer was replaced by methyl dihydroabietate.

Modifications of the invention will occur to persons skilled in the art. We, therefore, do not intend to be limited in the patent granted except as necessitated by the appended claims.

We claim:

1. The process of producing a negative ofiset printing plate from a plate comprising a base, a hydrophobic film of a copoiymer of a vinyl alkyl ether and maleic anhydride on said base, and an overcoating on said film of a light-sensitive, water-soluble diazonium compound which becomes insolubilized and ink-receptive in areas exposed to light, said compound being selected from the class consisting of those of the formulae:

wherein R is a radical selected from the group consisting of phenyl, aralkyl, cycloalkyl and acyl; Y is a member selected from the group consisting of O, S, NH, NR wherein R is an alkyl radical; Ar is an aromatic radical and X is the anion selected from the group consisting of an acid and the condensation products thereof with formaldehyde; said process comprising the steps of:

(a) exposing said plate to light under a pattern, and

(b) locally removing said overcoating Where unexposed by means of a developer containing an alkylolamine and a hydrophobic material which becomes physically attached to the tanned diazo resin layer in the image areas thereby rendering them hydrophobic and ink-receptive; while (c) simultaneously with (b) imparting a hydrophilic character to said film in areas Where the overcoating is removed.

2. The process according to claim 1 wherein the hydrophobic material in the developer is a high molecular weight fatty acid.

3. The process according to claim 1 wherein the hydrophobic material in the developer is a high molecular weight fatty alcohol.

4. The process according to claim 1 wherein the hydrophobic material in the developer is an aliphatic ester of a high molecular weight fatty acid.

5. The process accordingto claim 1 wherein the hydrophobic material in the developer is oleic acid.

6. The process according to claim 1 wherein the hydrophobic material in the developer is dimerized oleic acid.

7. The process according to claim 1 wherein the hydrophobic material in the developer is a mixture of linoleyl, linolenyl, oleyl, cetyl and stearyl alcohols.

8. The process according to claim 1 wherein the hydrophobic material in the developer is trioctyl phosphate.

References Cited in the file of this patent UNITED STATES PATENTS 2,667,415 Neugebauer et al Jan. 26, 1954 12 Herrick et al Dec. 4, 1956 Herrick et a1 Sept. 30, 1958 Seven et al. May 17, 1960 Herrick et a1. May 2, 1961 Straw et al July 25, 1961 Deal et a1 -5. Jan, 15, 1963 Case Apr. 9, 1963 FOREIGN PATENTS Great Britain Sept. 23, 1953 OTHER REFERENCES Conant et al.: The Chemistry of Organic Compounds, The MacMillan Co., New York, 4th ed., 1952, pages 203 15 and 211. 

1. THE PROCESS OF PRODUCING A NEGATIVE OFFSET PRINTING PLATE FROM A PLATE COMPRISING A BASE, A HYDROPHOLIC FILM OF A COPOLYMER OF A VINYL ALKYL ETHER AND MALEIC ANHYDRIDE ON SAID BASE, AND AN OVERCOATING ON SAID FILM OF A LIGHT-SENSITIVE, WATER-SOLUBLE DIAZONIUM COMPOUND WHICH BECOMES INSOLUBILIZED AND INK-RECEPTIVE IN AREAS EXPOSED TO LIGHT, SAID COMPOUND BEING SELECTED FROM THE CLASS CONSISTING OF THOSE OF THE FORMULAE: 